In recent years, printing apparatuses have successfully achieved color printing and digital printing, at high speeds. Nowadays the printer industry has focused on offset printing technologies, which have become the mainstream.
With in this field, a lot of requirements focus on binding paper sheets discharged after a printing process, for which various binding types are available. For example, case binding often used for manuals, textbooks, and the like is a binding method which glues a portion serving as the spine of a paper bundle (to be referred to as the main body hereinafter) printed by a printing apparatus, covering the main body with the cover, and binding it as a book.
For example, Japanese Patent Laid-Open No. 2002-283767 discloses a technique to cover the side edge and spine of a paper bundle on the cover surface side with a front cover, adhering a back cover to the front cover, and then pressing the adhered portion of the paper bundle to create a booklet. A known technique to generate a warning when a paper type is set in advance for a cassette which stores paper sheets, and no paper sheet of the designated type is set in the cassette upon designating the paper type is disclosed in Japanese Patent Laid-Open No. 2003-262994.
However, unexpected bound books may emerge if it is permitted to freely use paper sheets of different types for the cover and main body while performing case binding using the above-mentioned method. For example, when paper sheets used as a main body are thick (for example, one paper sheet is thick or the number of sheets is large), and a thin paper sheet is used as a cover for covering the main body, the bound book may bend. When paper sheets used for the main body are made of rigid material, a bound book will not endure the pressure unless the cover is made of a rigid material corresponding to the material of the main body.
Most of books treated in the printing industry have many pages, and the thickness of paper bundles varies. There are a variety of paper types used for the main body and cover. Hence, appropriate paper sheets must be selected from a variety of types in accordance with the thickness and paper type of the main body.